Fast warmup cathode



Match 11, 1969 J. SCHMIDT 3,432,714

FAST WARMUP CATHODE Filed Jan. 24, 1967 V l9 l2 Cr D i I /VVVWAANVWM/VWAM WVWVVWNWNVWMM WVVD IG l J 20 I4 20 FIG. I

Fred J. Schmidt INVEN'IIOR.

M .LW

Huh/TM al uji am United States Patent Oflice 3,432,114 Patented Mar. 11, 1969 3 Claims ABSTRACT OF THE DISCLOSURE A fast warmup cathode having a coil-coil heater embedded in a layer of bonding ceramic adjacent a layer of insulating ceramic which is bonded to the cathode lid, and a heater leg brazed to the coil-coil heater ensuring positive electrical contact between the heater coil and the heater leg.

BACKGROUND OF THE INVENTION Currently, fast warmup cathodes are fabricated by embedding a circular tungsten coil-coil heater into an insulating ceramic mix, attaching the leg to the coil by forming a hook on the end turns of the heater coil, placing an amount of metallic brazing material over the joint, and sintering the entire assembly at elevated temperature. The term, coil-coil heater, refers to a heater coil that is made by first coiling the heater wire about a mandrel approximately 3 millimeters in diameter and then coiling this coil into a suitable configuration such as a spiral in a plane parallel to the cathode lid.

In many instances (during high temperature processing), the insulation mix will glaze over the top of the heater coil turns immediately under the braze joint and insulate them from the metallic brazing material. This results in an immediate loss of electrical contact.

In other instances, the metallic braze material is loosened and lifted enough during heater cycling life test due to expansion and contraction of the leg material to cause loss of electrical contact within the first 2,000 or so cycles of life test.

SUMMARY OF THE INVENTION The heater coil is arranged in a spiral configuration in a plane parallel to the cathode lid. The end two or three turns of the coil-coil heater are turned up at a 90 bend to the main body of the coil, protruding above the level of the insulation mix and cannot become glazed and covered by the insulating material. The hook portion of the leg is still mounted around the end of the coil as before and the entire joint covered by a metallic brazing material. Now, however, at least two turns of the heater coil are actually protruding up through the metallic brazing material, thus, eliminating the possibility of the braze material pulling away from the exposed portion of the heater coil.

It is, therefore, an object of this invention to provide a fast warmup cathode that is not subject to the insulation mix glazing over the top of the heater coil turns during high temperature processing.

It is another object of this invention to provide a fast warmup cathode which during operation is not subject to the braze material loosening and lifting due to expansion and contraction of the leg material enough to cause loss of electrical contact.

BRIEF DESCRIPTION OF THE DRAWING The various features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects with its use, reference should be had to the accompanying drawing and descriptive matter in which is illustrated and described a preferred embodiment of the invention, and in which:

- FIGURE 1 is a diagrammatic view depicting a cathode constructed according to the present invention; and

'FIGURE 2 is a view partly in cross section of a portion of the cathode of FIGURE 1 showing in greater detail the components thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT The general arrangement of a preferred embodiment of a fast warmup cathode according to the present invention is illustrated in FIGURE 1 wherein a cathode lid 12 has a coil-coil type heater 14 secured thereto in such a manner as to assure positive electrical contact between the heater coil and heater legs 18.

Heater coil 14 is arranged in a spiral configuration in a plane parallel to cathode lid 12. The heater coil is embedded in a layer of bonding ceramic 16 which is bonded to a layer of insulating ceramic 10 which is in turn bonded to the cathode lid. In order to physically and electrically secure heater legs 18 to the heater coil, an amount of metallic brazing material is placed over the joint and the entire assembly is sintered at an elevated temperature.

The details of heater leg and heater coil connection are shown in FIGURE 2 wherein the heater coil 14 is shown to have a portion 14a comprising the last two or three turns turned up at a bend to the main body of the coil. The ends of the heater coil protrude through the bonding layer 16 and the body of brazing material 20. This protrusion of the heater coil prevents the bonding ceramic from glazing over and covering the heater coil. The hook portion 18a of the heater leg is mounted around the end 14a of the heater coil and covered by brazing material 20, however, since at least two turns of the heater coil are actually protruding up through the brazing material which eliminates the possibility of the braze material pulling away from the heater coil.

While in accordance with the provisions of the statutes I have illustrated and described the best form of the invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention as set forth in the appended claims, and that in some cases, certain features of the invention may sometimes be used to advantage without a corresponding use of other features. Accordingly, I desire the scope of my invention to be limited only by the appended claims.

I claim:

1. A fast warmup cathode comprising: a cathode lid; a layer of insulating ceramics bonded to said lid; a layer of bonding ceramic bonded to said insulating layer; a coil-coil heater embedded in said bonding ceramic; a plurality of coils at the ends of said heater being disposed at an angle with respect to the main body of said heater and protruding above the level of said bonding ceramics; a heater leg including a hook portion attached to and electrically connected to said coil-coil heater; a body of metallic brazing material covering the joint between said heater leg and said coil-coil heater.

2. A fast warmup cathode as set forth in claim 1 wherein said angularly disposed coils protrude through said body of brazing material.

3. A fast warmup cathode as set forth in claim 2 FOREIGN PATENTS wherein said hook portion of said heater leg lies in a 1 012 695 12/1965 Great Britain. plane parallel to that of the main body of said heater. 1:378:572 10/1964 France References Cite! 5 JOHN w. HUCKERT, Primary Examiner. UNITED STATES PATENTS A. J. JAMES, Assistant Examiner.

1,797,990 3/1931 Lucian 313--337 2,489,298 11/1949 Lafierty 317-270 X US. Cl. X.R.

3,175,118 3/1965 Ney 313-337 X 3l3270, 340

3,227,906 1/1966 Kuehne 313-270 X 10 

